Behavioural Ecology and Habitat use of the European Nightjar (Caprimulgus europaeus) during Stopover in Southern Sweden: A radiotracking study

Abstract

During the second half of August and the first part of September 2017, I radiotracked several European nightjars (Caprimulgus europaeus) around the Stensoffa area in Southern Sweden. Several locations were taken for each bird each night, including diurnal roost and nocturnal points composed by flying and resting behaviours. Being a long-distance migrator already on the way south during autumn migration, it was confirmed that the study place is a stopover area for the species. Along with other stopovers in their journey, those sites are key for the performance of the birds during migration, allowing them to replenish their fat storages between flight bouts. With the data of five individuals, I was able to show that they adjust the starting time of their nocturnal activity based on the change in sunset time, but not during the morning with the change on sunrise time, when other factors are also important. It was proven also, that roost locations are mainly inside forest patches not far from open areas where they feed. Compositional analysis for the habitat use of the birds studied showed a random use of the different habitats, contradicting my first thought. These individuals changed roost location on several occasions, something that was believed did not happen that often. All the birds left the area in south direction and during nights with good visibility after nights with bad weather. I conclude that the radiotracking work performed by one person, although not ideal, provides a good estimation of the locations of the birds during both day and night and gives valuable data for the study of the stopover ecology of a migratory bird species.

Popular Abstract

What do European nightjars do in Sweden just before migrating to Africa?

Every year after the breeding season ends, a substantial percentage of the European birds start preparing for the autumn migration that will lead them to Africa. There, birds will spend the winter in warmer locations with more resources for them. But getting there is not a direct journey. Along their migratory routes, birds will have several breaks between flight bouts at stopover areas to refuel the energy they spend flying. They stopover for several days and try to eat as much as possible until they are ready to continue their way south, repeating this process many times until they arrive at their final destination. The importance of the stopover sites is huge because the total time of migration is approximately divided in a 7:1 ratio between those breaks and the time in flight. Also, the energy spent at stopover is about twice that spent when flying in the global energy cost of migration. Thus, it is crucial to investigate and understand the birds’ habitat use in these areas because it can give us a lot of information about the ecology of bird migration. In addition, we can compare that with how birds behave and use the land at the other seasons of the year and identify similarities and differences as well as key areas of great importance for migratory birds.

Why nightjars?

European nightjars (Caprimulgus europaeus) travel one-way about 8000 kilometres from Sweden to Sub-Saharan Africa, an example of “long-distance migration”, at this time of the year and the same distance back in spring. As crepuscular aerial insectivores, they eat mainly moths, mosquitoes and other aerial insects at dusk and dawn, but also during the night. During the day, nightjars sleep at their roosting spots. There are no records of nightjars breeding at the study area, the surroundings of lake Krankesjön in Southern Sweden, a place dominated by grasslands adjacent to a mixture of coniferous and deciduous forest with some water bodies in the middle. Therefore, I was certain that the birds present there had already started their autumn migration. This is the kind of habitat this species lives in, with forest to spend the day and open areas to feed.

To study the movements of the birds, I used a traditional method for monitoring bird behaviour - radiotracking. I caught seven birds and attached them a tag with an antenna that transmits a signal to a receiver, giving me a rough estimate of their position. For more than two weeks, I followed five individuals around the study area to identify roosting locations and preferred feeding areas.

It was confirmed that my study area is a stopover site for European nightjars. One of the main results was that the birds got active earlier in the evening as the nights were starting earlier due to the advancement of dusk, but I could not confirm the opposite pattern in the morning. My data showed that roost locations had more forest around them than activity ones, confirming they sleep in the forest and go to open places to forage during the night. However, no habitat was found to be used more than others when the birds were active, probably due to the low number of individuals. I could also pinpoint a minimum of three and a maximum of seven roost locations for each bird, contradicting the common assumption that nightjars do not change their sleeping place that often. The birds only departed the study area in nights with good weather conditions after nights with rain.

Master’s Degree Project in Biology: Animal Ecology, 45 credits, 2018.
Department of Biology, Lund University.
Supervisors: Anders Hedenström and Gabriel Norevik

• author: Esteban, Arturo
• supervisor: Anders Hedenström; Gabriel Norevik
• organization: Degree Projects in Biology
• course: BION02 20172
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8960318
• date added to LUP: 2018-10-16 11:51:28
• date last changed: 2018-10-16 11:51:28